Gamma-ray Lines in the Fermi Data: is it a Bubble?

Abstract

Recently, tentative evidence for an excess of gamma rays at energies around 130 GeV has been reported from analyses of data from the Fermi Large Area Telescope (LAT). The excess is potentially of great interest, as it could be associated with the pair-annihilation of Galactic dark matter and the subsequent production of monochromatic or internal bremsstrahlung gamma rays. The 130 GeV excess appears when an optimized selection of the target region of interest is employed, a procedure that depends upon the assumed dark matter density profile. For the profiles producing an appreciable signal, these target regions vastly overlap with the region corresponding to the so-called "Fermi bubbles". We argue that the tentative evidence for a line feature is likely due to hard photons in the Fermi bubbles regions, where the gamma-ray spectrum contains a spectral break in the energy range of interest (100-150 GeV). Although the origin of this broken power-law is unclear, it is probably related to standard astrophysical processes and not to dark matter annihilation. A broken power-law provides as good a fit as a line "excess", even within small energy windows, and a significantly better fit for large energy windows.

v2: comments on recent analyses added; version to appear in JCAP

References in corpus (5)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
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Cited by in corpus (10)

• Gamma Ray Signals from Dark Matter: Concepts, Status and Prospects
• Fermi 130 GeV gamma-ray excess and dark matter annihilation in sub-haloes and in the Galactic centre
• Two Lines or Not Two Lines? That is the Question of Gamma Ray Spectra
• Three Exceptions for Thermal Dark Matter with Enhanced Annihilation to Gamma Gamma
• Statistical Issues in Astrophysical Searches for Particle Dark Matter
• Effect of Black Holes in Local Dwarf Spheroidal Galaxies on Gamma-Ray Constraints on Dark Matter Annihilation
• Searching for the continuum spectrum photons correlated to the 130 GeV gamma-ray line
• Galactic Center Radio Constraints on Gamma-Ray Lines from Dark Matter Annihilation
• Detection Potential of the KM3NeT Detector for High-Energy Neutrinos from the Fermi Bubbles
• On the possibility of a 130 GeV gamma-ray line from annihilating singlet fermionic dark matter